A small-sized mobile camera is installed in a camera-equipped mobile terminal. In this small-sized mobile camera, an auto focus (AF) lens holder driving device is used. VCM systems using a voice coil motor (VCM) are known as a driving mechanism (actuator) used for the above-mentioned AF lens holder driving device. An AF lens holder driving device of the VCM type includes a magnetic circuit composed of a driving coil, a yoke and a permanent magnet as a driving mechanism (actuator). The driving mechanism of the VCM type is roughly categorized into the driving mechanism of “moving coil type” and the driving mechanism of “moving magnet type.”
An AF lens holder driving device of the VCM type employs a spring member (elastic member) that supports a columnar movable part including a lens (a lens and a lens holder) such that the movable part is displaceable in the light axis direction (center axis direction) in a state where the position of the movable part in the radial direction with respect to the fixing part is set. It is to be noted that the movable part is also referred to as moving body, movable body, or lens fixing body, and the fixing part is also referred to as fixing member, supporting body, housing, or fixing body. The above-mentioned driving mechanism is provided in the movable part (moving body) and the fixing part (fixing member; supporting body).
As the above-mentioned spring member (elastic member), in general, a pair of leaf springs which are provided on the both sides in the light axis direction of a lens holder (columnar movable part; moving body) that holds a lens assembly (lens barrel) are used. The pair of leaf springs supports the lens holder (columnar movable part; moving body) such that the lens holder (columnar movable part; moving body) is displaceable in the light axis direction in a state where the position in the radial direction of the lens holder is set with respect to the housing (cylindrical fixing part; fixing member; supporting body) disposed at the periphery thereof. One of the pair of leaf springs is referred to as upper leaf spring, and the other is referred to as lower leaf spring.
It is to be noted that the upper leaf spring is also referred to as front spring or front spring member, and the lower leaf spring is also referred to as rear spring or rear spring member.
With the above-mentioned configuration, in an AF lens holder driving device of the VCM type, the restoration force (biasing force) of the leaf spring (spring member) and the thrust (driving force) of the driving mechanism are balanced, and the movable part (moving body) is moved to a predetermined position (target position) in the light axis direction. In the AF lens holder driving device of the VCM type having such a configuration, the movable part (moving body) is supported with the leaf spring (spring member) with respect to the fixing part (fixing member; housing; supporting body), and therefore the movable part (moving body) is vibrated more than necessary by driving of the movable part (moving body), or by vibration, impact and the like from the outside.
In view of this, a position detection part (position detection mechanism; position detection means) is provided to the lens holder driving device to control (adjust) the position of the movable part by feedback control. Conventionally, various position detection parts have been proposed.
For example, PTL 1 discloses a lens driving device that performs hand shake correction by utilizing a position detection mechanism using a Hall device sensor magnet and a Hall device sensor. The lens driving device disclosed in PTL 1 includes a cylindrical lens supporting body, an annular yoke, and a plurality of driving magnets. The cylindrical lens supporting body extends in the longitudinal direction and the coil is placed on the outer periphery side. The yoke is placed on the outside of the lens supporting body in the radial direction. The driving magnets are respectively placed at positions on the inside of the external peripheral wall of the annular peripheral wall of the yoke and the outside of the coil in the radial direction with a predetermined distance from the coil. In addition, the driving magnets are placed with a predetermined distance from the adjacent driving coil in the circumferential direction of the yoke.
In PTL 1, the Hall device sensor magnet is placed at the lens supporting body at a position between adjacent two driving magnets in the circumferential direction of the yoke in the driving magnets. The Hall device sensor is placed to a base to which the yoke and the lens supporting body are installed. A cutout part is formed in the driving magnet at the side surface opposite to the adjacent driving magnet.
PTL 2 discloses an image pickup device including an actuator and a position detection part. The actuator is composed of a coil attached on a driven surface of a movement cylindrical body that holds a plurality of lenses, a magnet opposite to the coil, and a yoke disposed at the periphery of the magnet. The position detection part is composed of one Hall device magnet attached on the movement cylindrical body, and a Hall device provided on an assembly housing side opposite to the movement cylindrical body and configured to detect the magnetic force of the Hall device magnet to perform position detection.
PTL 3 discloses a lens driving device including an actuator and a position detection means. The actuator includes a coil body fixed at the outer periphery of a lens supporting body that supports a lens at the inner periphery, a yoke that movably supports the lens supporting body, and four driving magnets fixed at corner portions of the outer periphery side wall of the yoke. The inner periphery side of each driving magnet has an arc-like shape extending along the outer peripheral surface of the coil.
In addition, in the third embodiment in PTL 3, the position detection means that detects the position of the lens supporting body with respect to the fixing body in the X direction, the Y direction and the Z direction is composed of a X-direction position detection magnet, a Y-direction position detection magnet, and a Z-direction position detection magnet disposed on the side surface of the lens supporting body, and, a X-direction position detection device, a Y-direction position detection device, and a Z-direction position detection device disposed on the external surface of the lens driving device so as to be respectively opposite to the direction position detection magnets.
It is to be noted that the Z-direction position detection magnet is magnetized to have opposite magnetic poles in the Z direction (light axis direction). To be more specific, when the driving magnet is magnetized such that the inner periphery side is N pole and the outer periphery side is S pole, the Z-direction position detection magnet is magnetized such that the front side (upper side) thereof is N pole and the rear side (lower side) thereof is S pole in the light axis direction. In the lens supporting body, a weight is fixed for the purpose of balancing the weight balance with the three position detection magnets. The position detection magnets and the weight are disposed at positions corresponding to the space part of the yoke.